For papermaking purposes, fibers from wood chips or other raw fiber source are ground into chips or mechanically treated such that the chips may be broken down further and refined into individual fibers.
Disc refiners are used to break down clumps of fibers into individual fibers in high density stock containing eighteen to sixty percent fiber by weight. Disc refiners are also used with low density, low consistency pulp of two to five percent fiber dry weight to increase the freeness or bonding capability of the individual fibers.
A refiner disc is a disc-shaped steel or steel-alloy casting which has an array of generally radially extending bars formed on the surface thereof. The disc refiner typically utilizes pairs of opposed refiner discs. One disc is mounted on a rotor for rotation. Another disc is held opposed to the first refiner disc, either by rigid mounting or by mounting on a rotor which turns in an opposite direction. Wood pulp is refined as it passes between the rotating opposed discs.
A refiner for high density stock employs an auger which is axially mounted with respect to the rotor on which the refining disk is mounted. A flinger nut may be positioned adjacent to the end of the auger which feeds the stock into a breaker bar section. The breaker bar section feeds the stock to the refiner disks where wood chips and clumps of fiber are broken down into individual fibers. Conventional refiner bar sections employ essentially radially extending rectilinear refiner bars on the rotor opposed by stationary essentially radially extending rectilinear bars mounted to the refiner housing.
In paper manufacture, the cost of power (electricity) and the cost of stock or wood fibers are the single largest component of the paper product's total cost. The paper fiber or stock is manufactured from wood chips which are in many respects an industrial commodity whose price is governed by the market and not easily controlled. Thus, to improve the cost and efficiency of the papermaking process, it is important to focus on reducing the cost of processing the wood chips used to produce the stock or furnish from which the paper is made. High consistency refiners used principally with mechanical or semi-chemical pulps are relatively large consumers of power. Therefore, any improvement of through-put or power utilization in the refiner can lead to significant cost and efficiency savings.
Furthermore, the vast volumes of stock which flow between the refiner discs inevitably results in wear of the refiner bars, eventually necessitating replacement of the individual refiner discs. Not only is the substitution of new refiner discs costly in terms of replacement parts, but it requires that the refiner be downed and taken out of service while the discs are replaced.
What is needed is a disc refiner which requires less frequent replacement of refiner discs, and which efficiently achieves desired pulp quality.